1. Technical Field of the Invention
The present invention relates to an exhaust apparatus for an engine. This apparatus accelerates the purifying reaction through a catalyst of exhaust gases from an engine that have been mixed with secondary air from the exterior, so that the exhaust gases are sufficiently purified. In addition the exhaust noise is reduced on output.
2. Related Technical Information
When exhaust gases are emitted from an engine which is being operated at an excessively rich air/fuel ratio, it has long been known to further accelerate the purifying reaction of such exhaust gases by passing them through a catalyst in a state in which they have been mixed with secondary air introduced from the exterior. When this secondary air is supplied to the exhaust system of the engine, means for forcibly increasing the flow velocity by a pump or the like is generally used. Such a means of supplying secondary air, however, must adjust the amount of supplied secondary air in accordance with the amount of emitted exhaust gases, by controlling it by a throttle valve or the like, but such control is comparatively complicated and thus the apparatus becomes larger and more expensive.
To solve this problem, each of Japanese Patent Laid-Open Publication Nos. 6-212964 and 7-19039 disclosed means for automatically introducing secondary air from the exterior, utilizing an ejector (entraining) effect induced by exhaust gases emitted from an engine. Such a secondary air introduction means has an advantage in that the negative pressure generated by the flow of exhaust gases sucks in secondary air from the exterior. This ensures that an amount of secondary air corresponding to the amount of emitted exhaust gases is introduced, so that there is no particular need for means of controlling the amount of secondary air that is introduced, thus simplifying the configuration.
However, the exhaust apparatus of each of these applications utilizes an ejector (entraining) effect using exhaust gases of a flow velocity that has been reduced after they have left a silencer chamber (expansion chamber), and a swirl tube is provided in order to swirl the exhaust gases and increase the flow velocity thereof. This increases the number of components, increasing the cost.
The present invention has the objective of providing an exhaust apparatus for an engine which is capable of using the ejector (entraining) effect of the exhaust gases to suck in secondary air efficiently, but which has a simple and inexpensive structure.